A wide range of methods and apparatus are known and have been widely utilized in the fixed biological film aerobic treatment and anaerobic treatment of aqueous liquors containing biodegradable waste products. The term "fixed film" refers to systems where the microorganisms are attached to the surface of a solid inert material as opposed to being freely suspended as e.g., agglomerated particles in a liquid medium.
There are basically three general categories of fixed film aerobic and anaerobic treatment processes, a submerged system, in which the fixed film is submerged in a aqueous liquor, a trickle-bed system which the fixed film is exposed to the atmosphere in aqueous liquors trickled over the film and a combination in which the fixed film is alternately immersed in an aqueous liquor, and then exposed to air or inert gas as is done in a rotating biological contacter. In the submerged fixed film category, the micro organisms are attached either to the surface of the immobile solid matrices or to mobile solid particles submerged in a aqueous liquor.
Representative patents which illustrate submerged fixed film and mobile matrix type systems for effecting biological degradation of waste products are shown in the following patents.
U.S. Pat. No. 3,966,608, illustrates a submerged technique for aerobically biologically treating waste products containing submerged packing, such as Raschig or Pall rings. The treatment zone utilizes a central column and adjacent oxidation zones in fluid communication with the central column. An aerating fan is located at the top of column to draw the liquor upwardly through the column and the waste sprayed outwardly over a packing to effect aeration thereof, and then caused to flow downwardly through the adjacent columns. The microorganisms which are fixed to the packing effect oxidation of the waste.
U.S. Pat. No. 3,235,234 illustrates a technique for treating waste, wherein a treatment zone is immersed in a tank containing waste, the treatment zone being filled with a porous packing such as saddles, wire mesh or corrugated sheets defining a serpentine path in the vertical direction. An oxygenating gas is introduced through a diffuser, such as a sparge unit, placed beneath the packing. Both waste and oxygenating gas are forced upwardly through the packing unit and the waste biologically digested.
U.S. Pat. No. 4,267,052 discloses a process an apparatus for aerating and circulating a liquid in a vessel utilizing a surface aerator and bottom mixing rotor mounted on a hollow common shaft. The combination of the surface aerator and submerged rotor permits good bottom mixing as well as aeration of the medium at the bottom of the tank for enhanced biological degradation.
U.S. Pat. No. 4,425,231 discloses a wastewater treating apparatus which includes a circulation type aeration tank, having both downward and upward flow chambers which communicate with each other at the upward and lower ends. An oxygenated gas is supplied to the downward flow chamber and wastewater and return sludge are supplied to a given position or elevation in the upward flow chamber such that a reduction zone with low concentration of dissolved oxygen is formed at the upper portion of the upper flow chamber.